[PATCH] support: Use unwinder in links-dso-program-c only with libgcc_s

[Florian Weimer]

* Frank Scheiner:

> Dear Florian,
>
> On 26.03.25 16:36, Florian Weimer wrote:
>> Do not build links-dso-program-c with exception (unwinding) support
>> if libgcc_s is not available.  In this case, the unwinder may be
>> part of libgcc.a or libgcc_eh.a, depending on how GCC was built.
>> If the unwinder is in libgcc_eh.a only, linking links-dso-program-c
>> failed before this change.  After this change, the exception
>> handling landing pad is only generated if libgcc_s available,
>> avoiding an undefined _Unwind_Resume (or equivalent) symbol
>> reference in the non-libgcc_s case.
>>
>> Fixes commit ffd36cc27407003a6f9efcb9c16370e3435c5b1d ("support: Use
>> unwinder in links-dso-program-c only with libgcc_s") and
>> commit 5dfbc3c43ecc1bcfc760a032c91bb002660051bc ("support: Link
>> links-dso-program-c with libgcc_s only if available").
>
> This seems to break our cross-builds for ia64 with T2 and IIUC also any
> cross builds in T2 for other architectures, starting with
> ffd36cc27407003a6f9efcb9c16370e3435c5b1d, where two extra lines were
> added to support/Makefile:

What is “this”?  You talk about
ffd36cc27407003a6f9efcb9c16370e3435c5b1d, but the patch is supposed to
fix that.

I've pushed this patch here (thanks Joseph for the quick review).
Please test again.

Thanks,
Florian